I've logged about 375 miles on Inov-8 f-Lite 230s, 95% on pavement, and have a trail 50K coming up in four weeks (North Face Endurance Challenge, Wisconsin). It's my first trail race and first ultra (ten marathons, several halfs).

At this point, do I dance with the one that brought me (the f-Lites), or is there a better trail shoe that I could break in sufficiently before the race?

I would stop running on your old shoes, break a new pair in (as long as they are the same kind, and safe and reliable for you) but then still use your old shoes during the race. At least that way though you'll have a backup pair in case anything goes wrong.

I mean, if you're logging 50 mpw or something like that you're gonna be able to log a lot of miles in new shoes in 2.5 weeks, even with a 1.5 week taper.

Just speaking from my experience, I bought a new pair of Brooks PureFlow about a month before my 50k and they were broken in just fine by the time my race rolled around. That's just my experience, but I think you would be fine if you did decide to get a new pair.